The invention relates to an improved encapsulating material for electronic components, to a method for protecting electronic components of an ink jet printhead and to ink jet printheads constructed using the encapsulating material.
Ink jet printers continue to evolve as the technology for ink jet printing continues to improve to provide higher speed, higher quality printers. The improvement in speed and quality does not come without a price, however. The printheads of such printers are more costly to manufacture and thus there is a movement to longer life permanent or semi-permanent printheads which are used in conjunction with replaceable ink cartridges.
With the movement to longer life permanent or semi-permanent printheads, there arises a need for improved methods of protecting the electrical components, particularly the flexible circuit or TAB circuit traces and the electrical connections between the traces and the substrate chips from ink corrosion. If the traces or electrical connections are not adequately protected from the ink, electrical shorts or inadequate electrical signals to the printhead could result.
A variety of ways for protecting the electrical circuits have been attempted. For example, PCT application No. WO 98/55316 filed May 26, 1998, describes the use of a latent curable film for use in bonding a flexible circuit to a pen body of an ink jet printer pen. The film is said to contain an epoxy material, a polyester component, a photoinitiator and a hydroxyl-containing material. According to the ""316 application, curing of the bonding film is initiated by exposing the film to ultraviolet radiation and the film then continues to cure at room temperature without further exposure to radiation. The amount of epoxy-containing material relative to the amount of the polyester component in the film is said to be selected depending on the properties such as film strength or film flexibility which are desired. Such bonding films therefore have a shelf-life once curing is initiated by the ultraviolet radiation which may not be adaptable to changes in manufacturing steps or procedures.
Despite advances made in the art of bonding electrical circuits to the pen bodies, there remains a need for improved formulations which provide enhanced protection of electrical components and greater flexibility with regard to manufacturing processes. Also as ink formulations also continue to improve, there is a need for more robust encapsulating materials which better withstand the corrosive properties of the improved ink formulations.
With regard to the foregoing and other object and advantages, the invention provides a dual curable encapsulant which includes from about 0 to about 20 percent by weight of a multifunctional epoxy material, from about 80 to about 95 percent by weight of a di-functional epoxy material, a catalytic amount of a photoinitiator and co-catalyst and a reactive diluent.
In another aspect the invention provides a method for protecting electrical traces on a flexible circuit or TAB circuit and connections between the traces and one or more printheads for an ink jet printer. The method includes applying a dual curable encapsulant to the flexible circuit or TAB circuit connections wherein the encapsulant contains from about 0 to about 20 percent by weight of a multifunctional epoxy material, from about 80 to about 95 percent by weight of a difunctional epoxy material, a catalytic amount of a photoinitiator and co-catalyst and a reactive diluent. After applying the encapsulant to the connections, at least a portion of the encapsulant is exposed to actinic radiation sufficient to initiate cross-linking between the difunctional and multifunctional epoxy materials and to cure at least portions of the encapsulant material exposed to actinic radiation. Heat is then applied to the encapsulant material at a temperture sufficient to cure any portion of the encapsulant material not exposed to the actinic radiation.
In yet another aspect the invention provides a pen for an ink jet printer. The pen includes a cartridge body containing one or more printheads attached thereto and one or more flexible circuits or TAB circuits attached to the one or more printheads. Each of the flexible circuits or TAB circuits contains electrical traces and electrical connections from the traces to the one or more printheads. An encapsulant encapsulates the connections, the encapsulant containing from about 0 to about 20 percent by weight of a multifunctional epoxy material, from about 80 to about 95 percent by weight of a di-functional epoxy material, a catalytic amount of a photoinitiator, a co-catalyst and a reactive diluent.
An advantage of the compositions and methods according to the invention is that ink jet pens may be assembled and critical electrical connections protected with an encapsulant that may be cured by actinic radiation or thermal energy alone or by a combination of actinic radiation and thermal energy. This is particularly useful for protecting parts which, when assembled are shielded or hidden from radiation sources which are used for curing such as when the encapsulant to be cured is disposed on the back side of the flexible circuit or TAB circuit between the circuit and the cartridge body. Another advantage of the invention is that it provides an encapsulant which may be cured an amount sufficient to enable handling of critical electrical parts during assembling of the printer components without loss or flow of encapsulant away from the desired location.
While not desiring to be limited by theory, it is believed the co-catalyst transforms or otherwise interacts with the photoinitiator to provide a unique initiator which enables the encapsulant to be cured by either actinic radiation or thermal energy.